Verify and repair

Pacman 3 gives you a facility for doing an extensive verification of the integrity of installed software after-the-fact. To see an example of this, do 

% pacman -install BU:Python
delete some files (e.g. the whole python directory) and do 
% pacman -verify
To see that errors are reported and do 
% pacman -repair
to see that Pacman is able to repair the damage.

Pacman Headquarters